In the United States we do not have 3G/HSPA/UMTS networks active anymore. I came to Canada recently and discovered that Canadian carriers do have 3G networks still active, which the Spitz supports connecting to. On the latest official firmware I noticed that after a while I would get kicked down to 3G after some time.

Luckily, just days after I'd arrived in Canada, GL-iNet released a snapshot firmware that included a new Operator Lock feature. The operators are listed along with each RAT they support. So you can lock onto their "4G" (which will also connect to NR NSA once established on LTE), or their 3G, and I assume if your SIM is SA-Enabled, a "5G" option would show up in the list too.

Simply setting the Operator Lock to "Manual-Auto" and choosing TELUS, Bell, or Rogers (4G) locked onto the correct network technology and I never experienced drops to 3G again, even after days of zero activity on the network.